docs: def Reynolds_valve(nu, Q, D1, FL, Fd, C):
      r'''Calculates Reynolds number of a control valve for a liquid or gas
      flowing through it at a specified Q, for a specified D1, FL, Fd, C, and
      with kinematic viscosity `nu` according to IEC 60534 calculations.
  
      .. math::
          Re_v = \frac{N_4 F_d Q}{\nu \sqrt{C F_L}}\left(\frac{F_L^2 C^2}
          {N_2D^4} +1\right)^{1/4}
  
      Parameters
      ----------
      nu : float
          Kinematic viscosity, [m^2/s]
      Q : float
          Volumetric flow rate of the fluid [m^3/s]
      D1 : float
          Diameter of the pipe before the valve [m]
      FL : float, optional
          Liquid pressure recovery factor of a control valve without attached 
          fittings []
      Fd : float
          Valve style modifier [-]
      C : float
          Metric Kv valve flow coefficient (flow rate of water at a pressure drop  
          of 1 bar) [m^3/hr]
  
      Returns
      -------
      Rev : float
          Valve reynolds number [-]
  
      Examples
      --------
      >>> Reynolds_valve(3.26e-07, 360, 150.0, 0.9, 0.46, 165)
      2966984.7525455453
  
      References
      ----------
      .. [1] IEC 60534-2-1 / ISA-75.01.01-2007
      '''
      return N4*Fd*Q/nu/(C*FL)**0.5*(FL**2*C**2/(N2*D1**4) + 1)**0.25